Variable buoyancy arrangement

ABSTRACT

A variable buoyancy arrangement includes a tank of fixed volume and pressure-regulating apparatus for maintaining the interior of the tank within a fixed pressure range above the ambient underwater condition. An air pressure actuated pump is selectively operable under user control for decreasing buoyancy by inserting water into the tank; and buoyancy may be increased by opening a stop valve to expel water from the tank.

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[54] VARIABLE BUYANCY [56] References Cited ARRANGEMENT UNITED STATES PATENTS [72] Inventor: mbmfl'mmphy wesfl'ianfmdcmn' 3,161,028 12/1964 Odum etal ..6l/69 11 [73] Assignee: The Wiremold Company, West Hartford, 3,487,647 1/1970 Brecht ..61/69 1R Conn. Primary Examiner-l Karl Bell 1221 F11ed= Sept-2911969 AttorneyDavis,1-1oxie,Faithfull&l-1apgood 21 Appl.No.: asawa [57] STU Related U'S'Applimmm Dam A variable buoyancy arrangement includes a tank of fixed [63] Continuatiomimpan of Sen 767373 Oct 14 volume and pressure-regulatipg apparatus for maintaining the 1968, Pat. No. 3,572,048, Continuation-impart of Ser. No. 766,932, Oct. 11, 1968, Pat. No. 3,541,985.

interior of the tank within a fixed pressure range above the ambient underwater condition. An air pressure actuated pump is selectively operable under user control for decreasing buoyancy by inserting water into the tank; and buoyancy may be increased by opening a stop valve to expel water from the tank.

13 Claims, 11 Drawing Figure PATENTEBraazz I972 Ill" INVENTOR. ROBERT M.

VAWABLE BUOYANCY ARRANGEMENT This application is a continuation-in-part of my pending application Ser. No. 767,373, filed Oct. 14, 1968, patented Mar. 23, 1971 U.S. Pat. No. 3,572,048 and also a continuation-inpart of my joint application Ser. No. 766,932, tiled Oct. 11, 1968 patented Nov. 24, 1970 US. Pat. No. 3,541,985.

This invention relates to apparatus carried by a person during underwater activities to control the aggregate buoyancy of himself and his equipment. The apparatus enables the diver to effect a desired buoyancy with respect to the depth of his activities and facilitates his ascent or descent in the water.

For underwater activities such as military demolition and hazard fabrication, salvage and treasure recovery, scuba explorations and the like, a diver is equipped with an air source for breathing, and typically loaded with sufficient weight to characterize the system comprising the diver and his equipment as having a neutral, or substantially neutral buoyancy. This permits the diver to move about, and to select his vertical water depth under his own physical power while expending energy only to overcome inertia and develop motion, and not to maintain a desired depth once it has been attained.

However, this weight selection process is only approximate at best. Further, when the buoyancy forces acting on the diver change, e.g., by decreasing when the volume of the diver and his equipment decreases under the influence of increased water pressure at greater depths, normally referred to as suit squeeze, or by increasing when theweight of the diver and his equipment decreases as his air is consumed (typically a change of several pounds), the diver; isforced to reduce or add to his weighting (or to change the volume of his equipment) to maintain a neutral buoyancy. This is often accomplished by picking up rocks from the water bottom and carrying the rocks about, clearly a cumbersome and insecure procedure.

Further, a diver must often swim significant distances at water level to go to and from a starting point such as an anchored craft to the desired diving area. Thus he must expend considerable energy swimming on the surface in a buoyancy condition much better suited to underwater swimming.

It is thus an object of the present invention to provide improved underwater maneuvering apparatus.

More specifically, an object of the present invention is the provision of apparatus for selectively varying the buoyancy of the diver and his apparatus without employing cumbersome weighting elements.

These and other objects of the present invention are realized in an illustrative variable buoyancy-control apparatus adapted to be physically carried by the diver during his underwater activities. The apparatus includes a tank of fixed volume having as one input thereto a valve configuration for maintaining the interior of the tank at an air pressure within a fixed narrow range above that of the ambient environment. A pushbutton actuated valve is employed to selectively actuate a water pump, with the pump being responsive to each depres sion of the valve button for inserting a fixed quantity of water into the tank chamber. The tank includes an operator-controlled stop valve for selectively expelling water from the tank, the water being discharged under the action of the above-ambient internal tank pressure when the stop valve is opened.

The user of the above apparatus may decrease its buoyancy as changing conditions from time to time dictate by depressing the valve actuating button, thereby causing the pump to force additional water into the tank chamber. Since the chamber is of fixed volume, the weight of the additional water displacing an equal volume of much lighter air in the tank supplies an incremental downward force in absence of additional water displacement. The added water alters the ration of water volume :to air volume in the tank. But, since the chamber is of fixed volume, the amount of water displaced by the tank and not counteracted by water within the tank is lessened, thereby decreasing the buoyancy. correspondingly, to increase the system buoyancy by a desired amount, the stop valve is opened and water is forced out of the pressurized chamber, thus reducing the system weight, while its volume remains constant. Swimming along the water surface is facilitated since the chamber can be purged of water and thus act as a flotation aid.

A complete understanding of the present invention, and of the above and other features and advantages thereof may be gained from a consideration of the detailed description of an illustrative embodiment thereof presented hereinbelow, in conjunction with the accompanying drawing which depicts in schematic form a variable underwater buoyancy arrangement.

Referring now to the drawing, a variable buoyancy arrangement there shown includes a tank 12 which is adapted to exhibit a constant volume when the inside thereof is pressured. The tank 112 may thus be fabricated either of a rigid material such as metal or a hard synthetic plastic, or of an air-inflatable material such as canvas which will not stretch beyond a fully expanded volume. Any desired shape will suffice for the tank 112, although a form contoured for comfortable mounting on the back of the user about the users air supply cylinder is most convenient.

To supply air under higher than ambient underwater environmental pressure, an air source it) is provided. in the preferred form illustrated, this is the main air cylinder carried for underwater breathing purposes which commonly contains air under a pressure of several hundred pounds per square inch. Before reaching the tank T2 in the manner discussed below, the high-pressure air is supplied to a pressure regulating valve 15 which reduces the air pressure to a relatively low level, e.g., to about pounds per square inch above the ambient underwater pressure for delivery to four branch conduits 116, 117, 18 and 19. One air conduit llti leads to the users breathing apparatus, a second conduit 17 conveys air to a stop valve me via a valve 116 for selectively expelling water from the tank 12; the third conduit lid leads to a valve 2t1 which, when actuated, operates a pump Sil for inserting a fixed charge of water into the tank 12; and the fourth conduit 59 conveys pressurized air to valve apparatus sass-9s for maintaining the interior of the tank 112 within a fixed pressure range (e.g., 3-5 p.s.i.) above the ambient underwater pressure.

To insert water into the tank chamber l2, thereby decreasing diver buoyancy, a pump 50 is adapted to insert a fixed quantity of water into the tank 112 each time it is operated by the valve 20. The pump 50 is advantageously located within the tank, although it may be externally mounted and coupled to the tank by suitable conduits. The pump 50 includes a cylinder 52 having a drive piston 54 which slides therein. A connecting rod 56 connects the drive piston 54- with a follower piston 58 having a plurality of ports 62 therein. The ports 62 are sealed by a flapper (check) valve member 60 during the active pumping stroke. A pump housing 5 ll includes a plurality of ports 53 therein through which water passes into the tank 12 during an active pump stroke. The ports 53 are sealed by a flapper (check) valve member 66 which seals these ports under urging of the internal tank pressure at all other times.

A passageway 7d connects the pump to the underwater medium. Two conduits 32 and 34 are connected to the pump cylinder 52 on either side of the piston 56, and connect the piston cylinder to a slide valve 20 which is selectively operated by a pushbutton 21 biased by a spring 22 to a rest position.

The valve 26 includes a slide member 36, having three apertures 38, ill and t2 thereon, for selectively connecting one of the conduits 32 or 34 to the relatively high air pressure output of the regulator valve 15 via the conduit 1%, and for venting the other conduit 32 or 314i to the underwater medium through one of two exhaust orifices 26 or 2% which are open to the ocean. In particular, with the valve 2 ll in its normal inactive state as shown in the drawing, the slide aperture 40 connects the conduit 32 to the pressurized tube 1th, and the aperture 3% connects the conduit M to the exhaust port 28. Correspondingly, when the valve 20 is operated by depressing the button 2ll, aperture 42 vents conduit 32 via port 26, and the valve i5 supplies air pressure to the conduit 341.

With the valve 20 in its rest position, the pressure above the piston 54 (that generated by the regulating valve l5) exceeds H ll! the ambient pressure beneath the piston, and the piston 54 resides at the bottom of the cylinder 52 against a stop 55. Water flows through the passageway 74 and around the follower piston (indicated by vector 70) into the pump housing 51. The water is prevented from flowing through the pump exit ports 53 by the flapper 66 which is maintained against the ports 53 by the internal tank pressure.

To insert the water residing in the pump housing 51 into the tank 12, the valve 20 operating button 21 is depressed. As discussed above, this couples a relatively high pressure to the bottom of the drive piston 54 via conduit 34, while venting the cylinder 52 above the piston 54. Accordingly, the piston 54, along with the connecting rod 56 and the follower piston 58, are forced upward toward a stop 55 During this active pumping stroke, the follower piston 58 and its covering flapper member 60 create a pressure which forces water through the ports 53 and into a tank chamber, while forcing the flapper member 66 away from the exit side of the ports 53, as to the dashed position 66 shown in the drawing. The volume of water inserted in the tank is essentially given by the cross-sectional area of the tank housing 51 multiplied by the length of the active piston stroke, i.e., the height of the cylinder between the stops 55 and 55. At the end of the active stroke, the pump no longer exerts a pressure on the flapper 66 which is returned to a position sealing the ports 53 by the internal tank pressure.

When the valve operating button 21 is released, and thereby reset to its normal position by the spring 22, the pressure gradient between the conduits 32 and 34 is reversed, and an excess of pressure above the driving piston 54 resets it to its normal, or rest position against the stop 55. The connecting rod 56 forces the follower piston 58 along with its flexible flapper member 60 to their downward normal position.

Water is drawn into the pump housing 51 beneath the piston 58 during the active stroke when the tank 12 is being charged. On the return stroke for the follower piston 58, water flows through the ports 72 in the piston and around the flapper member 60 which is forced away from the piston to the dashed position 60 shown in the drawing. in addition, water flows around the follower piston 58. Thus, following the return stroke, water is again disposed into the pump housing 51 between the follower elements 58-60 and the pump exit ports 53 to discharge into the tank 12 during the next actuation of the valve 20.

A three-way slide valve 116 is employed to operate a stop valve 106 for selectively expelling water from the tank 12. The valve 106 includes a valve housing 136 and pressure-sensitive diaphragm 108. The stop valve housing 136 includes ports 110 through which water may selectively enter from the tank 12, and a discharge passageway 115 leading to the underwater medium. A conduit 104 is normally Thus, by the valve 116 to the relatively high-pressure output of the regulator valve 15 to bias the diaphragm 108 downward over the ports 110 (dashed position 108' in the drawing) hence preventing water from flowing from the tank 12 into the interior of the valve 106. When the valve 116 is operated, the conduit 104 is vented to the ambient medium and the diaphragm 108 is raised to the dash-dotted position 108" by the internal pressure of the tank 12, whereupon water flows from the tank through the ports 110 and is discharged through the passageway 115. Thus, water is continuously expelled from the tank 12 as long as the conduit 104 is vented.

The slide valve 1 16 includes an operating button 118 which is biased to an external rest position by a spring 120. The valve includes a slide member 124 with an aperture 126 thereon. When the button 118 is not activated, the aperture 126 connects the conduits 17 and 104 thus forcing the stop valve diaphragm 108 downward and sealing the valve ports 110. When the button 118 is depressed, the aperture 126 connects the conduit 104 with a valve venting port 130 thereby opening the water discharge path 110-115 as considered hereinabove.

To maintain the interior of the tank within a fixed pressure range above the ambient medium (e.g., 3-5 p.s.i. as discussed above), a three-way valve 86 includes a slide member 90 which is selectively operated by a differential pressure-responsive regulating valve 80. The valve includes a diaphragm 82 having one side exposed to the underwater medium, and the other side connected to the interior of the tank 12 by a port 81. The pressure of the underwater medium is increased by a spring 83 which adds an additional pressure in the range 3-5 p.s.1.

When the interior tank 12 pressure beneath the diaphragm 82 is approximately equal to the pressure on top of the diaphragm 82 (at a level given by the underwater ambient pressure plus the spring pressure), a connecting rod 84 connected to the diaphragm positions the slide member in the three-way valve 86 to a neutral position. in this neutral position a valve 86 output conduit 96 is connected to neither the output of the regulator valve 15 via a conduit 19, nor to the ambient medium via a conduit 92.

Should the interior tank pressure become less than the desired pressure, the diaphragm 82 is forced downward by the spring 83 and the underwater medium. This, in turn, forces the valve 86 slide member 90 downward such that an aperture 93 in the slide member 90 connects the output conduit 96 with the pressurized conduit 19. When this condition obtains, air flows through the conduit 96, through a valve 98 and into the tank via two tubes 111 and 112. After sufficient air is inserted in the tank, the pressure coupled to the bottom of the diaphragm 82 via the valve port 81 returns the diaphragm 82 to its normal position, thereby resetting the slide member 90 to its neutral rest position hence disconnecting the conduit 96 from the pressurized conduit 19.

If the interior pressure of the tank increases above the desired pressure (e.g., when the diver is rising such that the ambient pressure decreases, or when the pump 50 is actuated decreasing the residual air volume thus increasing its pressure) the port 81 couples a net positive pressure to the bottom of the diaphragm 82 thereby raising this member, along with the connecting rod 84 and the valve slide member 90. The slide aperture 93 then connects the conduit 96 with the venting conduit 92 such that air flows out of the tank via one of the conduits 111 or 112 (depending upon the orientation of the tank) and through the valve 98. Air is continuously vented until the pressures on both sides of the diaphragm 82 are equalized to maintain the slide member 90 in its neutral position.

The orientation sensitive three-way valve 98 and the two conduits 111 and 112 having their ends located in opposite portions of the tank 12 are employed to connect the conduit 96 with the vertically raised part of the tank which has air in it, and not to the lower tank portion which contains water. This selection permits the pressure in the tank 12 to be maintained within the desired range by removing air and not water when the internal tank pressure is to be reduced.

The position sensitive three-way valve 98 and the conduits 111 and 112 are described in detail in said application Ser. No. 767,373, filed Oct. 14, 1968, now US. Pat. No. 3,572,048, the disclosure of which is made part hereof. In brief, the valve 98 includes a housing 100 having end chambers 10] and 117, and a central chamber 113 connected to conduit 96. The chamber 101 comprises the space between the end of the housing 100 and an annular ring 105, while the chamber 117 is disposed between the other end of the housing 100 and an annular ring 114. Two balls 102 and 103 are respectively disposed in the compartments 101 and 117 and selectively seal central apertures 107 and 109 in the annular rings 105 and 114, respectively, depending upon the orientation of the valve 98 as discussed below. The tube 11 1 connects the valve 98 compartment 101 to the bottom portion of the tank 12, and the tubing 1 12 connects the upper portion of the tank 12 to the valve compartment 117.

When the tank 12 resides in the vertical orientation shown in the drawing, the ball 102 rests on the annular member 105 sealing the aperture 107 in this annular member. Accordingly, the ball 102 disconnects the conduit 111, having its free end disposed in the water-containing lower portion of the tank 112, from the conduit 96. Correspondingly, the ball W3 rests on the bottom of the housing Mill, and the conduits 9b and M2 are thereby connected via the valve compartments M7 and llllll and the unblocked center 109 of the annular member lid. Since water resides on the bottom of the tank when it is in the position shown in the drawing, the conduit an is connected by the valve 9% and the tube 1B2 with the air containing upper portion of the tank 12.

When the tank is rotated to reverse the vertical orientation of the drawing (e.g., a diver descending head first), the ball W3 will rest on the ring lid and seal the aperture W9. This isolates the conduit 96 from the tube llil2 having its end now disposed in the water in the tank. Correspondingly, the ball 102 resides against the valve housing Mill, and the conduit 96 is thus connected to the conduit lilll which terminates in the air containing portion of the tank.

The balls T02 and W3 are physically proportioned, along with their seats 1105 and 1M, apertures ill? and 109, and the center chamber 113, so that they cannot both be in a. seated position at the same time because of interference.

Thus, the valves $0, an and 953, having the several conduits associated therewith, operate to maintain the interior of the tank within the desired pressure range of 3-5 p.s.i. above ambient by selectively increasing or decreasing the air pressure within the tank 12 irrespective of the orientation of the tank.

Finally, the tank contains a relief valve 76 which is adapted to open as a safety measure should the pressure within the tank exceed a predetermined limit for any reason (cg, l p.s.i. above the ambient medium).

With the above arrangement in mind, an illustrative sequence of operation for the buoyancy-controlling apparatus will now be described. A diver just beginning his journey starts with his tank 12 substantially free of water and with an internal pressure between 3-5 pounds per square inch above ambient, as produced by the output of the regulator valve 15 acting through the conduit 19 and the valves d0, db and 9d. The user swims on the water surface to the diving area with the empty tank being a flotation aid and not an encumbering weight which has to be transported.

At the diving location, the diver repeatedly actuates the button 21 to change his status from positive to neutral or slightly negative buoyancy. With each depression of the button 21, the pump 50 responds in the above-described manner to air pressure from the regulator valve 15 which drives the piston S ll via the valve 2t by forcing a fixed quantity of water through the tank ports 53 and into the tank 112. Since the tank 12 is of a fixed volume it displaces a like fixed volume of water when submerged. Thus, when water is introduced into the tank by the pump t), the weight of this water directly subtracts from the fixed buoyancy force acting on the user and his submerged equipment, which again is of a fixed volume.

At neutral or slightly negative buoyancy, the diver is free to move about underwater as he desires without expending energy to maintain his underwater depth. As the buoyancy of the diver and his equipment decreases, e.g., because of increased water pressure as he moves to greater depths, he may compensate by releasing some of the water pumped in at the surface to begin his dive. Correspondingly, as his buoyancy increases because the user expends his air supply or moves to shallower water with less pressure and less suit squeeze, the user simply pushes the button 21 to inject more water into the tank 12.

For any orientation of the diver and the tank H, the valve 9i connects the conduit lllll or ill?! tenninating in the air-containing portion of the tank 12; to the conduit 96. The diaphragm 82 and spring 83 normally position the valve as slide member 90 to a neutral position, and move the slide member to connect the conduit 96 via the conduit 92 or W to reduce or increase the tank pressure, respectively, if it departs from the desired value. Accordingly, the valve arrangement till, as and 9h maintains the interior of the tank within the desired pressure range for any water depth and corresponding ambient pressure, and for any orientation of the diver. Since the internal tank pressure is maintained at a few p.s.i. above ambient, the tank is not crushed at great water depths, even when fabricated of materials which are not normally form retaining or which do not possess sufficient inherent mechanical strength to withstand the ambient underwater pressures which may be extremely large.

When the diver wishes to increase his buoyancy, either as an assistance in rising or to correct for an overweighted condition, he depresses the button lllld to operate the stop valve 11%. The internal pressure of the tank forces water in the tank 1?; through the valve apertures ill) and out the passageway llllS into the underwater medium while maintaining the diaphragm litlh in a position away from the apertures till). Water continuously flows out of the tank until the button llllh is released to again apply pressure from the conduit lll to the conduit M4 to force the diaphragm W8 downward to seal the ports llllll. As water is expelled, the downward weight force acting against the buoyancy force is continuously decreased thereby increasing net buoyancy.

if at any time the interior of the tank becomes overly pressurized, the relief valve 76 opens to vent the excessive air pressure.

Thus, the variable buoyancy arrangement depicted in the drawing and disclosed in detail above is readily operable under control of the user to generate any desired buoyancy condition for the user and his equipment vis-a-vis the sur rounding underwater environment.

The arrangement described above is only illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention. For example, the variable buoyancy apparatus may be used to help a diver carry heavy objects picked up on the bottom, or it may be attached to heavy objects to be transported for maintaining their buoyancy regardless of changing depths without the instability inherent in buoyancy tanks open to the sea.

What is claimed is:

ll. in combination in a variable buoyancy arrangement adapted for underwater activity, a tank of substantially fixed volume for selectively storing water, means for maintaining the interior of said tank at a pressure which exceeds the un derwater ambient pressure, means for selectively introducing water into said tank, and means for selectively discharging water from said tank, wherein said selective water-introducing means comprises a pump having a discharge port connected to said tank, said pump including a cylinder, a drive piston having first and second surfaces, said drive piston being mounted for sliding translation within said cylinder, a pump chamber, a follower piston connected to said drive piston and located in said pump chamber, and means for selectively impressing a pressure gradient in said pump cylinder about said first and second driving piston surfaces.

2. A combination as in claim 1 further comprising check valve means connected to said pump discharge port.

3. A combination as in claim 2 wherein said check valve means includes flexible flapper-sealing means located over said pump discharge port.

i. A combination as in claim 3 further comprising check valve means included on said follower piston.

5. A combination as in claim i wherein said follower piston check valve means includes apertures in said follower piston, and a flexible flapper-sealing means disposed over said apertures.

ti. A combination as in claim 2 wherein said pressure gradient impressing means includes first and second conduits connected to said pump cylinder on opposite sides of said drive piston; a valve including an input port to be energized with pressurized air; at least one venting port, and means for alternately connecting one of said conduits connected to said pump cylinder to said pressurised valve port and for connecting the other of said conduits to said venting port.

7. In combination in a variable buoyancy arrangement adapted for underwater activity, a tank of substantially fixed volume for selectively storing water, means for maintaining the interior of said tank within a predetermined pressure range above the underwater ambient pressure, means for selectively introducing water into said tank, and means for selectively discharging water from said tank, wherein said tank interior pressure-maintaining means includes input means adapted for connection to a source of compressed air, venting means, first valve means for selectively connecting said tank to one of said air supplying input means or to said venting means, and differential pressure valve means responsive to the pressure differential between the interior and exterior of said tank means for selectively operating said first valve means.

8. A combination as in claim 7 further comprising orientation-responsive valve means for connecting said first valve means to the upper portion of said tank.

9. A combination as in claim 7 wherein said first valve means includes a slide member for selectively connecting said tank to said air input means, and wherein said differential pressure valve means includes a diaphragm having two surfaces respectively exposed to the environment outside said tank and to the interior of said tank, and means connecting said diaphragm with said slide member of said first valve means.

10. A combination as in claim 9 further comprising spring means for biasing said diaphragm.

11. A combination as in claim 7 wherein said waterdischarging means including stop valve means comprising at least one input port and at least one exit port, a diaphragm for selectively sealing said input port, and additional valve means for selectively operating said diaphragm.

12. A combination as in claim 11 wherein said additional valve means includes a vent port, an air input port, a transferred port connected to said stop valve means, and slide means for selectively connecting said transferred port to said vent port or to said air input port.

13. A combination as in claim 8 wherein said orientationresponsive valve means includes three aligned compartments separated by two annular members each having a central orifice therein, ball means in the two end compartments for selectively sealing the central aperture in at most one of said annular members depending upon the orientation of said valve means, first conduit means connecting the central valve compartment with said first valve means, and additional conduit means connecting the end valve compartments with differing portions of said tank such that the portion of said tank oriented vertically upward is operatively connected by said additional conduit means and said orientation responsive valve means to said first conduit means.

:MMA 

1. In combination in a variable buoyancy arrangement adapted for underwater activity, a tank of substantially fixed volume for selectively storing water, means for maintaining the interior of said tank at a pressure which exceeds the underwater ambient pressure, means for selectively introducing water into said tank, and means for selectively discharging water from said tank, wherein said selective water-introducing means comprises a pump having a discharge port connected to said tank, said pump including a cylinder, a drive piston having first and second surfaces, said drive piston being mounted for sliding translation within said cylinder, a pump chamber, a follower piston connected to said drive piston and located in said pump chamber, and means for selectively impressing a pressure gradient in said pump cylinder about said first and second driving piston surfaces.
 2. A combination as in claim 1 further comprising check valve means connected to said pump discharge port.
 3. A combination as in claim 2 wherein said check valve means includes flexible flapper-sealing means located over said pump discharge port.
 4. A combination as in claim 3 further comprising check valve means included on said follower piston.
 5. A combination as in claim 4 wherein said follower piston check valve means includes apertures in said follower piston, and a flexible flapper-sealing means disposed over said apertures.
 6. A combination as in claim 2 wherein said pressure gradient impressing means includes first and second conduits connected to said pump cylinder on opposite sides of said drive piston; a valve including an input port to be energized with pressurized air; at least one venting port, and means for alternately connecting one of said conduits connected to said pump cylinder to said pressurized valve port and for connecting the other of said conduits to said venting port.
 7. In combination in a variable buoyancy arrangement adapted for underwater activity, a tank of substantially fixed volume for selectively storing water, means for maintaining the interior of said tank within a predetermined pressure range above the underwater ambient pressure, means for selectively introducing water into said tank, and means for selectively discharging water from said tank, wherein said tank interior pressure-maintaining means includes input means adapted for connection to a source of compressed air, venting means, first valve means for selectively connecting said tank to one of said air supplying input means or to said venting means, and differential pressure valve means responsive to the pressure differential between the interior and exterior of said tank means for selectively operating said first valve means.
 8. A combination as in claim 7 further comprising orientation-responsive valve means for connecting said first valve means to the upper portion of said tank.
 9. A combination as in claim 7 wherein said first valve means includes a slide member for selectively connecting said tank to said air input means, and wherein said differential pressure valve means includes a diaphragm having two surfaces respectively exposed to the environment outside said tank and to the interior of said tank, and means connecting said diaphragm with said slide member of said first valve means.
 10. A combination as in claim 9 furTher comprising spring means for biasing said diaphragm.
 11. A combination as in claim 7 wherein said water-discharging means including stop valve means comprising at least one input port and at least one exit port, a diaphragm for selectively sealing said input port, and additional valve means for selectively operating said diaphragm.
 12. A combination as in claim 11 wherein said additional valve means includes a vent port, an air input port, a transferred port connected to said stop valve means, and slide means for selectively connecting said transferred port to said vent port or to said air input port.
 13. A combination as in claim 8 wherein said orientation-responsive valve means includes three aligned compartments separated by two annular members each having a central orifice therein, ball means in the two end compartments for selectively sealing the central aperture in at most one of said annular members depending upon the orientation of said valve means, first conduit means connecting the central valve compartment with said first valve means, and additional conduit means connecting the end valve compartments with differing portions of said tank such that the portion of said tank oriented vertically upward is operatively connected by said additional conduit means and said orientation responsive valve means to said first conduit means. 